To make containers, and in particular metal cans, a tool pack is typically used in conjunction with a ram and a punch in a body-maker to form the container. A cup-shaped can blank is inserted into the tool pack such that the punch engages the blank and then forces the blank through a series of dies to iron the sidewalls of the container. After the sidewalls are ironed and thus formed to their finished thickness, the punch moves the container into a final die for the formation of a domed end. During the formation of the container, it is of great importance to maintain a linear (typically horizontal) pathway for the ram and punch. Any variance from a linear path can result in sidewalls of the container being formed with variations in thickness and unequal strength characteristics leading to possible unexpected failure. Because containers must be formed with the minimum thickness of the sidewalls being sufficient to meet predetermined strength requirements, containers are frequently made with portions of the sidewalls actually being thicker than required in order to ensure that no portion be less than the minimum required thickness. As in many industries, the cost of raw materials is a substantial concern for the manufacturers of containers. Therefore, any extra material that must be used to form the can is an unnecessary expense as well as a waste of the material.
Several devices have been developed to attempt to maintain a linear pathway for the ram and punch. One such device provides a support for a reciprocating ram utilizing a plurality of rollers. Typically, three rollers positioned 120.degree. apart support and guide a ram having ground surfaces to coincide with the rollers. The ram, which originally had a circular cross-section, must be ground to provide flat surfaces thereon to ride on the rollers. The grinding process must be performed with great precision and, consequently, increases the cost of the system. Two of the rollers are fixed in position while a third roller is provided with a spring to allow adjustability and to help keep the ram in contact with the other two rollers. However, due to a less than perfectly linear drive system, some degree of loping (or up and down motion) may be transferred to the ram which may cause the ram to vary slightly from a perfectly linear path. Such non-linear motion causes uneven sidewall thicknesses and tends to wear the ground surfaces on the ram as well as the roller surfaces, reducing the useful life of both. Additionally, the forming and drawing dies may wear unevenly, reducing their lives, and in a worse case, the punch may actually contact one or more of the dies causing damage thereto. Maintenance and repair as a result of such wear or damage can require removal of the entire guidance system for reworking, causing lengthy and expensive downtime. Also as can be appreciated, handling a heavy guidance system can present a safety risk to the personnel involved.
Other devices utilize a liquid bearing assembly for use with either a three shaft arrangement or a single ram arrangement. In either case, the ram is guided by liquid bearings rather than rollers. In theory, such a system provides increased ability to maintain a linear pathway for the ram due to a more uniform pressure on the entire ram circumference. However, in operation, liquid bearings are extremely difficult to maintain and are subject to leakage problems.
Thus, an apparatus is required which enhances the linearity of the pathway of the ram without the inherent difficulties of the prior art.